Graphics Programs Reference
In-Depth Information
• Lossless compression mechanisms suitable for image data and general data com-
pression, such as Flate (The zip algorithm), Lempel-Ziv-Welch (LZW) and run
length encoding.
Who Uses PDF?
PDF is used in a wide variety of industries and professions. We describe some here,
explaining why PDF is suitable for each.
The Printing Industry
PDF has support for the color spaces, page dimension information (such as media,
crop, art and bleed boxes), trapping support, and resolution-independence required
for commercial printing. Together with other technologies, PDF is the key part of the
publishing-for-print workflow. The extensibility of PDF metadata allows various
schemes for including extra data along with the document, and for keeping it with the
document throughout the publishing process—parts of the workflow which don't un-
derstand a particular piece of metadata will at least preserve it.
Ebooks and Publishing
This topic was created using the
DocBook
system, which takes a structured document
in XML format, typesets it, and produces a PDF complete with hyperlinks and book-
marks, together with a more traditional PDF suitable for printing.
PDF is one of the competing eBook formats. To support display on a wide range of
screens, PDF documents may be tagged with reflow information, allowing lines of text
to be displayed at differing widths on each device. This is at odds with the other uses
of PDF, where fixed text layout is a requirement.
PDF Forms
PDF forms are especially useful when existing paper-based systems are being transi-
tioned to electronic ones, or must exist alongside them. A PDF form (filled in online
then printed out) looks the same as one filled in manually on paper, and may be pro-
cessed by existing human and computer systems in the same way.
Automatic submission of forms from within the PDF viewer, the use of JavaScript to
add intelligence (making sure figures add up in a tax form, for example), and the use
of digital signatures to sign filled-in forms are all compelling reasons to use PDF for
electronic forms.
